When an impulse voltage such as lightning surge enters a stationary induction apparatus such as a transformer or reactor, the potential distribution in a winding becomes steep compared with the potential distribution that corresponds to the number of turns, and then, oscillations occur around the potential distribution corresponding to the number of turns. This phenomenon is referred to as potential oscillations. If potential oscillations have a large amplitude, a dielectric breakdown may occur due to a large potential difference generated between adjacent electric wires in a winding and between adjacent windings. When electrostatic shields are installed adjacent to windings, the electrostatic capacity between the windings becomes larger than the electrostatic capacity between the winding and the ground, thus reducing the amplitude of potential oscillations.
Japanese Utility Model Laying-Open No. 60-113614 (Patent Document 1) is a prior art document that discloses a transformer including electrostatic shields. In the transformer described in Patent Document 1, the electrostatic shields are provided at opposite ends of the winding in their central axes. Each of the outer peripheral ends and inner peripheral ends of the electrostatic shields is formed as a curved surface. The electrostatic shield is fixedly fastened to the winding in the central axis direction of the winding and has a width substantially identical to the width of the winding in the radial direction.